JPH0718325B2 - Ceramic valve - Google Patents

Description

TECHNICAL FIELD The present invention relates to a ceramic valve in which an intake and exhaust valve is made of ceramic.

[Prior Art] In recent years, internal combustion engines have become high-speed and high-powered, and it has been proposed that they be made of ceramics such as silicon nitride that are lightweight and have excellent heat resistance.

[Problems to be Solved by the Invention] Ceramics such as silicon nitride are brittle materials, and when the valve bouncing or jumping at a high rotation speed, it is immediately damaged in the radial direction at the position A or B in FIG. was there. In addition, the cylinder head may be deformed and damaged at the position C due to long-term use.

[Means for Solving the Problems] In order to solve the above problems, the ceramic valve of the present invention performs Si ₃ N intake or exhaust in the engine combustion chamber.
_{4 In a} ceramic valve made of a sintered body, the valve is formed by injection molding a granulated powder obtained by adding 5 to 20% by weight of a reinforcing member such as a fiber or whiskers made of a ceramic material to Si ₃ N ₄ powder. The structure in which the reinforcing member is formed and disposed along at least the axial direction is adopted as a technical means.

Further, the present invention adopts, as an embodiment, a ceramic valve of technical means characterized in that the reinforcing member such as the fiber or the whisker is located on the surface side of the valve.

[Operation and Effect of the Invention] According to the present invention configured as described above, the reliability of the ceramic valve which is lightweight and has excellent heat resistance is enhanced, and by using this valve, it is possible to achieve matching with the engine. It is possible to make high-performance engines such as low fuel consumption, high output, and low noise. Further, since the present invention has been proposed to be made of ceramics such as a piston pin and a connecting rod for the purpose of weight reduction, it can be applied to other parts. The critical bouncing amount and jumping amount at which the valve breaks increased, and the radial breaking strength of the stem of the ceramic valve increased. Further, the strength against damage to the joint portion of the stem with the valve body due to deformation of the cylinder head after long-term use was increased.

[Embodiment] First, each embodiment of the present invention will be described with reference to the drawings.

First, in the first embodiment shown in FIG. 1, reference numeral 1 denotes an exhaust valve for an engine combustion chamber, which will be described later, and comprises a valve body 1a and a cylindrical stem 1b. An annular groove 2 located at the upper end is formed in the stem 1b of the valve 1. 3 is a metal cotter, as shown in Fig. 2,
It is a wedge type with an arcuate cross-section and is a two-piece type of hug type, and is generally cylindrical. Such a cotter 3 is mounted on the stem 1b of the valve 1, and a ridge 3a having a semicircular cross section located in the groove 2 is integrally formed on the inner peripheral surface along the circumferential direction. Reference numeral 4 denotes a retainer which is fitted to the outer peripheral surface of the cotter 3 and which is made of, for example, a ceramic such as silicon nitride or a metal, and which is composed of an annular portion 4a and a flange portion 4b whose inside is a mounting hole, and the inner periphery of the annular portion 4a. The surface is tapered in the direction opposite to the outer peripheral surface of the cotter 3.

Now, the bulb 1 is made high in weight by placing 5 to 20 wt% of whiskers or fibers 50 such as SiC in a ceramic mainly composed of Si ₃ N ₄ which is lightweight and has excellent heat resistance, and is arranged in the axial direction. Make a ceramic with high strength and toughness (see Fig. 1).

Even if the whiskers or the fibers 50 are arranged only near the surface 1c in the axial direction of the bulb 1 as shown in FIG. 5, a sufficient effect for strengthening can be obtained. The whiskers or fibers can be easily arranged in the axial direction by molding a valve by injection molding.

As a background to this structure, it is possible to use conventional ceramics to increase the stem diameter of the valve, increase the radius of the back of the umbrella, and build up the pad. There is a circumstance that we do not want to use these methods as much as possible because the intake / exhaust passages are made narrower as well as being reduced.

The valve 1 having such a structure is attached to the cylinder head 5 of the engine as shown in FIG. A valve spring 6 is provided between the valve 1 and the cylinder head 5, and the valve 1 is axially urged upward by the spring 6 so that the valve element 1a passes through the exhaust passage 8 via the valve seat 7. It is hermetically closed. At this time, the retainer 4 comes into contact with the cotter 3 by a so-called wedge effect due to the taper of the retainer 4 depending on the state of the urging state of the valve spring 6 in the above-described direction, and thus firmly through the cotter 3 to the outer peripheral surface of the stem 1b. Will come into contact.

However, when the engine is operating, the valve 1 is displaced vertically in the axial direction to repeatedly engage and disengage the valve body 1a with respect to the valve seat 7, thereby alternately opening and closing the exhaust passage 8.

Next, the manufacturing method of the valve 1 will be described.

Example (1) 10 wt% Y ₂ O ₃ and 6 wt% Al ₂ O ₃ sintering aid were added to Si ₃ N ₄ , and further up to 30 wt% SiC whiskers (thickness 0.4 μm, length 30 μm
m) was added, and the mixture was wet mixed and then spray-dried to obtain a dry granulated powder. A binder for injection molding was added to this granulated powder, and after mixing, injection molding was performed to prepare a valve-formed molded body having a predetermined shape. After degreasing the molding binder, the compacted Si3N4 based ceramic valve with a shaft diameter of 6 mm in which SiC whiskers were aligned in the axial direction was obtained by firing in pressurized nitrogen of 70 atm at 750 ° C. for 4 hrs.

For comparison, a molded body having the same composition was prepared by the rubber press molding method and sintered under the same conditions. The SiC whiskers of this sintered body were not dispersed in the direction and were uniformly dispersed.

The ceramic valve thus obtained was evaluated under actual conditions under the following conditions. The results are shown in Table 1. (The cycle is set as shown in FIG. 6).

Experiment method Idle-free full load 7 seconds 5 seconds Example (2) A base material for injection molding was prepared in the same manner as in Example (1).
Then, a two-color molding method was used to arrange a base material not containing SiC whiskers on the inside and a base material to which SiC whiskers were added on the outside, and then both base materials were simultaneously injection-molded to obtain a green molded body containing SiC whiskers only near the surface. Degreasing and firing were performed in the same manner as in Example (1) to obtain a dense Si ₃ N ₄ -based ceramic valve. As shown in FIG. 5, it was confirmed that SiC whiskers were axially aligned from the surface to a thickness of about 1 mm in the obtained sintered body. The ceramic valve thus obtained was also evaluated in the actual machine under the same conditions as in Example (1). The results are shown in Table 2.

Example (3) A base material for injection molding was prepared in the same manner as in Example (1).
First, a base material not containing SiC whiskers was injection-molded to form a valve-forming shape having a diameter smaller than a predetermined shape by about 1 mm. Then, the obtained green body was placed in the center of the injection mold as a core, and injection molding was performed so as to cover the surface of the base material containing SiC whiskers. Degreasing continuously
Firing was performed to obtain a dense Si ₃ N ₄ -based ceramic valve with a shaft diameter of about 6 mm. In the obtained sintered body, it was confirmed that SiC whiskers were axially aligned from the surface to a thickness of about 1 mm as in Example (2). The ceramic valve thus obtained was also evaluated in the actual machine under the same conditions as in Example (1). The results are shown in Table 3.

Although the good results as described above have been obtained, when a conventional silicon nitride ceramic valve was prepared and used in an actual machine, it was placed at a portion (hatched portion) shown in FIG. 7 in a direction perpendicular to the axial direction. It might break. In order to increase the fracture resistance and improve the reliability, we tried to compound with SiC fiber. At first, it was molded by the rubber press method and tried to sinter. However, the effective amount that can be the resistance against vertical fracture is 1/3 of the added amount because the fibers are three-dimensionally uniformly dispersed.
Since it is about 1/5, more than 20 wt% of SiC fiber is required to fully exert its effect, and it is difficult to sinter by normal pressure sintering, pressure atmosphere sintering or HIP sintering. . On the other hand, in the injection molding method, since the fibers are aligned in the axial direction, it was found that the entire amount of addition works effectively and the effect can be exhibited at about 5 to 20%.

If the amount of SiC fiber added is less than 5%, the effect will not be obtained. 2
Greater than 0 wt% is not desirable because the sinterability deteriorates.

In addition, since the fracture generally occurs from the surface, if the SiC fiber is arranged only near the surface of the valve, sufficient effect can be obtained for strengthening. Further, it is desirable for the valve to be reinforced from the shaft end to the valve seat surface, because chipping or the like due to the inclusion of foreign matter on the lower surface of the valve is also considered.

Next, a supplementary explanation will be given as follows regarding the configuration in which the valve is applied to the engine.

Reference numeral 9 is a tubular valve guide that passes through the stem 1b of the valve 1, 10 is a cam connected to the shaft 11, 12 is a swing arm with which the cam 10 abuts from the upper end, one end of which is the stem.
It abuts on the upper end of 1b and the other end is supported by a spherical fulcrum.
14 is a valve for intake, this is the intake seat 15 valve seat
It has a function of opening and closing through 16, and is configured similarly to the exhaust valve 1. 17 is a valve guide, 18 is a valve spring, 19 is a swing arm, one end of which is a valve
The upper end of 14 is abutted and the other end is supported by the spherical fulcrum 20. Reference numeral 21 denotes a cam connected to the shaft 22, which is in contact with the swing arm 19. 23 is a cylinder block, 24
Is a piston for moving up and down in the cylinder block 23.

Although the ridges of the cotter are formed to have a semicircular cross section in each of the above embodiments, the ridges may be formed in any shape such as a rectangular shape without being restricted by this shape. In this case, it goes without saying that the cross-sectional shape of the groove in the valve stem also corresponds to the ridge.

In addition, in other words, it is needless to say that various changes can be made without departing from the spirit of the invention in concrete and practical implementation.

[Brief description of drawings]

1 to 4 show a first embodiment of the present invention,
1 is a longitudinal sectional view thereof, FIG. 2 is a longitudinal sectional view of a cotter, FIG. 3 is a sectional view of a retainer, FIG. 4 is a longitudinal sectional view of an essential part applied to an engine, and FIG. 5 is a longitudinal sectional view of the present invention. FIG. 6 is a longitudinal sectional view showing a second embodiment, FIG. 6 is an explanatory view, and FIG. 7 is a conventional explanatory view. In the figure, 1 ... Valve, b ... Stem, 1a ... Valve body, 2 ...
… Groove, 3 …… Cotta, 3a …… Ridge, 4 …… Retainer, 50 …… Whisker or fiber

Claims (2)

[Claims] 1. A ceramic valve made of a Si ₃ N ₄ sintered body for intake or exhaust in an engine combustion chamber, wherein the valve comprises a reinforcing member such as a fiber or whiskers made of ceramic material in Si ₃ N ₄ powder. A ceramic valve, characterized in that 5 to 20% by weight of granulated powder added and mixed is formed by injection molding, and the reinforcing member is arranged at least along the axial direction. 2. A ceramic valve according to claim 1, wherein the reinforcing member such as the fiber or whisker is located on the surface side of the valve.